SiO.sub.2 layer grown by liquid phase deposition (LPD) at room temperature not only has a low residual stress but also is advantageous in the fabrication of various semiconductor devices which requires a low fabrication temperature, such as the fabrication of LCD and 3-dimensional IC devices.
In U.S. Pat. No. 4,468,420, H. Kawahara et al. first disclose a method for making a silicon dioxide coating which comprises dipping a substrate in a mixed solution obtained by adding boric acid to an aqueous silicon dioxide-saturated solution of hydrofluosilicic acid. One of the present inventors, Ching-Fa Yeh, and his co-workers, in their article, entitled "Performance and Off-State Current Mechanisms of Low-Temperature Processed Polysilicon Thin Film Transistors with Liquid Phase Deposited SiO.sub.2 Gate Insulator", C.F. Yeh, S.S. Lin, T.Z. Yang, C.L. Chen and Y.C. Yang, IEEE Trans. on Electron Devices, Vol. 41, pp. 173-179, 1994, have successfully used a SiO.sub.2 grown by this liquid phase deposition (LPD) technique as a gate dielectric in a poly-Si thin film transistor which shows satisfactory electrical characteristics. However, the breakdown field strength of the LPD-SiO.sub.2 film is about 7-8 MV/cm and the interface trap density at the LPD-SiO.sub.2 /Si interface is about 5.times.10.sup.11 eV.sup.-1 cm.sup.-2, which still can be improved in comparison with a thermal SiO.sub.2 film.
S. Yoshitomi, S. Tomlika and N. Honeji in their article, entitled "The Characteristics of Si MOS Diodes Using the SiO.sub.2 Films Prepared by the Liquid Phase Deposition", International. EDMS, pp. 22.about.25, 1992, disclose a thermal annealing process to enhance the properties of the SiO.sub.2 films grown by the liquid phase deposition, in which annealing in O.sub.2 at a temperature of 400.degree. C. is found to be effective to improve the characteristics of the LPD-SiO.sub.2 film.